U.S. Pat. No. 3,825,432, West German Patent OLS No. 2,262,127, and Japanese Patent Publication No. 38245/76 disclose various fluoran derivatives as dye precursors for pressure-sensitive paper or heat-sensitive paper. However, such known fluoran derivatives do not provide deep black images. In addition, the fluoran derivatives themselves are unstable in the atmosphere and dyes produced therefrom show poor fastness to light, humidity, etc.